Different effects of thinning and burning on Sierran mixed-conifer ecosystems

1. Different effects of thinning and burning on Sierran mixed-conifer ecosystems Malcolm North, USFS, Sierra Nevada Research Center, Davis, CA

2. Focus and Scale of Some of the Fuel Reduction Experiments in California Large-scale fire movement & behavior, spotted owls LANDSCAPE (up to 500,000 ac) PLUMAS / LASSEN STUDY Water flow & nutrients; forest carnivores; birds; uneven-aged mgt. WATERSHED (3000-5000 ac) KINGS RIVER PROJECT STUDY SCALE FUNCTION / PROCESS FIRE SURROGATE STUDY STAND (50-100 ac) Stand dynamics, regene., management options; animals w/small home ranges Soils; microclimate; respiration; succession; food webs ECOSYSTEM (10 ac) TEAKETTLE EXPERIMENT

3. 1998 1999 2000 2001 2002 2003 2004 Pretreatment data (2-3 yrs for all studies) Treatments Post-treatment data(2-3 yrs for all studies) Monitoring (5-20 yrs)  Teakettle Location, Design, Plot Layout and Timeline 18 plots, 4 ha each, 3 reps of each of the 6 treatments • Burned November 2001, ‘off season’, for containment & air quality

4. Thinning Effects (using all trees in a 4 ha plot) Overstory (shelterwood): Thin > 25 cm & leave 22 large tree/ha Understory: 25 cm< thin < 76 cm

5. Teakettle’s Focus: Ecosystem Structure, Composition and Function

6. Collaborators

7. Teakettle Results: Focus on 4 Vegetation Questions Relevant to Developing Thinning and Burning Prescriptions • What effect do shrubs have on forest succession and water dynamics? • Why is mixed conifer so strongly clustered? Are trees grouped by age cohorts? • Do significant reductions in canopy cover reduce regeneration survival and understory herb cover? • Did the fire and thinning treatments produce a desired diameter distribution?

8. Forest 90 80 70 60 Mycorrhizae Exclosure 50 Root Exclosure 40 Control 30 20 Jul-02 Oct-02 Jun-02 Sep-02 Nov-02 Aug-02 May-02 100 Overstory trees 80 60 Tree saplings Percent of deep water used 40 Shrub 20 (Arctostaphylos spp.) 0 May June July August (using isotope signatures of soil and plant water) 1. What effect do shrubs have on forest succession and water dynamics? • Low tree seedling survival in shrubs and without root exclosure • Saplings and shrubs compete for shallow water in early summer • Trees rely on deep water through summer drought From A. Plaemboeck • Shrubs become islands that can ‘lock’ a site against seedlings and herbs

9. 5 4 3 2 L(t) 1 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 -1 Distance (m) 2. Why is mixed conifer so strongly clustered? Are trees grouped by age cohorts? Bonnicksen and Stone (1982) suggested pattern is due to grouped cohort age structure clustered

10. Are trees grouped by age cohorts? • No: ages were not spatially autocorrelated (variogram not shown)

11. Krigged distribution of tree basal area in a 4 ha area Why is mixed conifer so strongly clustered? • One influence may be that tree groups reflect the geomorphic template (depth to bedrock) Note correlation between the grouping of tree basal area, mostly driven by clusters of large trees and the depth to bedrock Depth to bedrock for the a 4 ha area, where deeper soils are in red. (Determined by seismic survey)

12. * 50 50 * 45 45 40 40 35 35 * 30 30 ALL ALL 25 25 Percentage Percentage DEAD DEAD 20 20 15 15 * 10 10 5 5 0 0 0 - 100 0 - 100 100 - 500 100 - 500 500 - 2000 500 - 2000 >2000 >2000 High Density Classes Low High Density Classes Low How Might This Explain Current Mortality Patterns? • Mortality episodic: associated with La Nina droughts • Most mortality in areas of high density • Significantly higher than expected mortality for large trees • Are small/intermediate trees depleting deep soil water pockets? * Significantly different than expected (Chi-square)

13. 3. Do significant reductions in canopy cover reduce regeneration survival and understory herb cover? Surface temperature by Julian date (y axis) and hour (x axis) for 3% and 76% canopy cover Persistent gaps in mixed-conifer without regeneration and having few herbs

14. Post-treatment: Germinant Survivorship • Burned treatments had higher pine germinant survival • Burn and thin treatments (BC and BS) also had the lowest white fir and incense-cedar survivorship • Herb cover and richness (not shown) significantly greater in all burned vs. thinned treatments, regardless of canopy cover reduction

15. Axis 2 Increased Micro-site Heterogeneity Data and slide from Harold Zald and Andy Gray, PNW Research • Increased separation of sugar pine and white fir based on light level • and soil moisture Post-Treatment Pre-Treatment Light Light Soil H2O Soil H2O

16. 4. Did the fire and thinning treatments produce a desired diameter distribution? Current diameter distribution Before fire suppression (1865) recruitment and mortality was ‘pulsed’ by fire and El Nino events

17. VTM* (‘desired’ dist.) 0.6 Control Burn.only Understory.only Understory...Burn Overstory.only Overstory...Burn 0.4 Proportion 0.2 0.0 10-30 31-60 61-90 >90 Size Class (cm) • Did the fire and thinning treatments produce a desired diameter distribution? • No: Not enough small and too many intermediate size trees taken * VTM is >2400 vegetation type mapping plots collected in the early ’30’s

18. What did we learn at Teakettle? • Thinning alone ‘stalls’ herb development and does not favor shade-intolerant regeneration • Fire’s important for reducing shrubs which are strong competitors with trees and herbs • Group selection doesn’t appear to be needed • Thinning treatments may need to target small trees in high density areas, particularly around large, old trees • If prescribed fire is applied ‘off season’, thinning must be aggressive about cutting small trees • Observation: Thinning prescriptions should stay focused on trees as fuels rather diameters or board feet